/**
 * Keeps a rolling twelve-month window of public holidays in the local cache.
 *
 * Idempotent by construction: running it twice leaves exactly what running it
 * once did. The one field it never touches on an existing row is
 * `isAutoClosed` — that is the shop's decision, not the API's, and a nightly
 * job quietly reopening a day the owner had closed would be the worst kind of
 * bug: invisible until someone finds the door locked.
 */

import { prisma } from '@/lib/db';
import { addCivilDays, toCivilDate, type CivilDate } from '@/lib/schedule/civil';
import { loadSettings } from '@/lib/schedule/context';

import { fetchHolidays, withRetries, type ParsedHoliday } from './openholidays';

export const SYNC_KEY = 'holidays';

export type SyncOutcome =
  | { ok: true; created: number; updated: number; removed: number; from: CivilDate; to: CivilDate }
  | { ok: false; error: string };

export type SyncDeps = {
  fetcher?: (options: {
    baseUrl: string;
    countryIsoCode: string;
    subdivisionCode: string;
    validFrom: CivilDate;
    validTo: CivilDate;
  }) => Promise<ParsedHoliday[]>;
  now?: Date;
};

export async function syncHolidays(deps: SyncDeps = {}): Promise<SyncOutcome> {
  const now = deps.now ?? new Date();
  const settings = await loadSettings();
  const today = toCivilDate(now, settings.timezone);
  const from = today;
  const to = addCivilDays(today, 365);

  const options = {
    baseUrl: process.env.HOLIDAYS_API_URL ?? 'https://openholidaysapi.org',
    countryIsoCode: settings.countryIsoCode,
    subdivisionCode: settings.subdivisionCode,
    validFrom: from,
    validTo: to,
  };

  let holidays: ParsedHoliday[];
  try {
    const fetcher = deps.fetcher ?? ((input) => fetchHolidays(input));
    holidays = await withRetries(() => fetcher(options));
  } catch (error) {
    const message = error instanceof Error ? error.message : String(error);
    await prisma.syncState.upsert({
      where: { key: SYNC_KEY },
      update: { lastErrorAt: now, lastError: message.slice(0, 500) },
      create: { key: SYNC_KEY, lastErrorAt: now, lastError: message.slice(0, 500) },
    });
    // The local cache is left exactly as it was: a stale calendar beats none.
    return { ok: false, error: message };
  }

  const existing = await prisma.publicHoliday.findMany({
    where: {
      subdivisionCode: settings.subdivisionCode,
      date: { gte: asDate(from), lte: asDate(to) },
    },
  });
  const existingByDate = new Map(existing.map((row) => [asCivil(row.date), row]));

  let created = 0;
  let updated = 0;

  for (const holiday of holidays) {
    const current = existingByDate.get(holiday.date);
    if (current) {
      const changed =
        current.nameFr !== holiday.nameFr ||
        current.nameEn !== holiday.nameEn ||
        current.nationwide !== holiday.nationwide;
      if (changed) {
        updated += 1;
      }
      await prisma.publicHoliday.update({
        where: { id: current.id },
        data: {
          nameFr: holiday.nameFr,
          nameEn: holiday.nameEn,
          nationwide: holiday.nationwide,
          syncedAt: now,
          // isAutoClosed deliberately absent: the shop owns that choice.
        },
      });
    } else {
      created += 1;
      await prisma.publicHoliday.create({
        data: {
          date: asDate(holiday.date),
          nameFr: holiday.nameFr,
          nameEn: holiday.nameEn,
          nationwide: holiday.nationwide,
          subdivisionCode: settings.subdivisionCode,
          syncedAt: now,
        },
      });
    }
  }

  // Days the API no longer lists — a cancelled or corrected holiday.
  const fetchedDates = new Set(holidays.map((holiday) => holiday.date));
  const stale = existing.filter((row) => !fetchedDates.has(asCivil(row.date)));
  if (stale.length > 0) {
    await prisma.publicHoliday.deleteMany({ where: { id: { in: stale.map((row) => row.id) } } });
  }

  await prisma.syncState.upsert({
    where: { key: SYNC_KEY },
    update: { lastSuccessAt: now, lastErrorAt: null, lastError: null },
    create: { key: SYNC_KEY, lastSuccessAt: now },
  });

  return { ok: true, created, updated, removed: stale.length, from, to };
}

function asCivil(value: Date): CivilDate {
  return value.toISOString().slice(0, 10);
}

function asDate(value: CivilDate): Date {
  return new Date(`${value}T00:00:00.000Z`);
}